Thermoregulation is fully developed in 5 day old Wilson's storm petrels Oceanites oceanicus (Kuhl). Resting metabolic rate (RMR) and body temperature (Tb) of unattended 1- and 3-day old chicks continuously decrease at ambient temperature (Ta) of 5°C. After being heated the chicks return to normothermia. Ability to survive temporal deep hypothermia seems to be an adaptation to absence of parents and low temperatures in the nest during first days of life. After snow storm, during two days of starvation, chick RMR decreases by 40% at Ta of 0°C, but chick Tb is stable. This suggest decrease of thermal conductance (Ct). Fall of Ct may suggest beginning of hypohermia.